The pressure bonding process and apparatus described in the above-identified cross-referenced applications, the disclosures of which are incorporated herein by reference, apply high frequency induction heating to the cooperating interface portions of metal components to be joined from within the space between them prior to a high energy rate impacting operation. The high frequency induction heating, which is characterized by localized surface heating, is largely dependent upon the surface area to be heated and the distance between the high frequency induction heating coil and the surfaces to be heated. Thus, for a given power output and configuration of the heating coil, the larger the interface surface area, the slower the heat-up rate. Similarly, the closer the heating coil is to the surface, the faster and more shallow will be the heating. If the heat-up rates and cross-sectional shapes of the mating components are not taken into consideration in the application of the induction heat, irregular and undesirable bonding can occur.
In addition to such problem of relative heating, there is an additional problem when bonding a component of irregular cross section, especially one which includes segments of cross-sectional area significantly different from other segments of that interface portion. Typical examples include bonding of airfoils to their bases and the jointing of "T" shapes and "L" shapes where very large differences in cross-sectional area exist. In such cases, it is important that the thickness/upset ratio be held constant through the entire joint. If such ratio is not held constant, the thin areas will overheat or will over-upset, or both, causing them either to buckle or to telescope or shingle over the mating component.